Heating unit

ABSTRACT

An in situ heating unit is provided by embedding an electric heating element in a flexible laminar structure impregnated with partially polymerized high-temperature-resistant resin. The object to be heated is easily and conformably wrapped in the laminate and electric current passed through the heating element to cure the resin, providing a low cost, adherent, void-free, efficient heating unit which is resistant to elevated temperatures and physical abuse.

United States Patent 1 Falk [ June 19, 1973 [73] Assignee: GeneralElectric Company,

Schenectady, NY.

[22] Filed: Nov. 1, 1971 [21] Appl. No.: 194,740

[52] US. Cl 219/535, 219/536, 219/549 [51] Int. Cl. H05b 3/58 [58] Fieldof Search 219/535, 528, 536,

[56] References Cited UNITED STATES PATENTS 2,559,077 7/1951 Johnson eta1 1 219/528 X 2,710,909 6/1955 Logan et al..... 338/212 2,741,6924/1956 Luke 219/528 2,938,992 5/1960 Crump 219/528 3,218,436 11/1965Edwards et al. 219/544 3,344,385 9/1967 Bartos et al 338/212 3,387,3336/1968 Irvine et al 219/528 X 3,657,517 4/1972 Hoyt 219/535 3,281,57910/1966 Glicksman.... 219/535 3,296,415 1/1967 Eisler 219/385 3,446,9095/1969 Kahn 219/535 X Primary Examiner-Volodymyr Y. MayewskyAttorney-Howard l. Schlansker and Arthur V. Puccini [57] ABSTRACT An insitu heating unit is provided by embedding an electric heating elementin a flexible laminar structure impregnated with partially polymerizedhigh-temperature-resistant resin. The object to be heated is easily andconformably wrapped in the laminate and electric current passed throughthe heating element to cure the resin, providing a low cost, adherent,void-free, efficient heating unit which is resistant to elevatedtemperatures and physical abuse.

1 Claim, No Drawings HEATING UNIT This invention relates to heatingunits. More particularly, the invention relates to economical heatingunits which are easy to fabricate, are adaptable to any shaped structurewhich is to be heated, and are resistant to elevated temperatures and tophysical abuse.

The use of heating units for various shaped structures or vessels inwhich the heating unit is made conformable to the surface of thestructure to be heated is well known. In some cases the heating unit ofa heatresistant fabric such as that of asbestos or otherhigh-temperature-resistant material such as certain polyamides and thelike is tailored and shaped to fit the particular surface, heatingelements of electrical resistance wire or carbonaceous or otherconductive material being used as the heating element proper. It is alsowell known to prepare such units in the form of, for example, anasbestos tape which has therein an electric heating element, the tapebeing wound about the structure to be heated in as closely a conformablemanner as'possible. Such prior art heating units are generally ratherexpensive, especially where they are tailored to fit a particular shape.They are furthermore relatively short-lived in that the fabric materialis subject to tearing and easy deterioration as well as shorting in thecase of certain spills such as with water solutions. Despite the caretaken in fitting such heating units to a structure, there are inevitablyleft within the unit and between the unit and the structure voids whichdetract from the heating efficiency. It is therefore a principal objectof the present invention to provide new and useful heating units whichare economical, are readily fitted to any particular shaped structure toprovide a closely adhering, void-free unit which, when thehigh-temperature-resistant impregnating resin is cured, is permanent innature and resistant to elevated temperatures and physicaldeterioration.

Those features of the invention which are believed to be novel are setforth with particularity in the claims appended hereto. The inventionwill, however, be better understood and further objects and advantagesappreciated from a consideration of the following description.

Briefly, the present invention consists of laminates of heat-resistantmaterial having embedded therein heating elements and impregnated with apartially polymerized hightemperature-resistant resin which is thereaction product of unsaturated bisimide with polyamine. The laminate isreadily wrapped in sheet, tape, or other suitable form around astructure to be heated of any desired shape in intimate contact with thesurface of the structure to provide good heat transfer, or the heatingunit can be entirely constructed on the object to be heated. When inplace, an electric current is passed through the heating element oroutside heat applied to complete the cure of the resinous impregnantproviding on the structure a heating unit which is permanent andefficient.

The resinous materials which are useful in connection with the presentinvention include those described in U.S. Pat. No. 3,562,223, Feb. 9,1971, such patent being incorporated herein. Generally, the polymericmaterials which are useful are derived from the reaction of unsaturatedbisimides and polyamines. The bisimide can be expressed by the formulawhere R is a member selected from the class consisting of the III and

groupings, and halogenated, e.g., chlorinated derivatives of formulasIll and IV containing up to six or more halogens, Q is a member selectedfrom the class consisting of divalent organic radicals of at least twocarbon atoms (both halogenated and unhalogenated) including but notlimited to, e.g., divalent hydrocarbon radicals of up to 40 carbonatoms, and divalent groups consisting of two aryl residues attached toeach other through the medium of a member selected from the classconsisting of an alkylene radical of from one to 10 carbon atoms S, SO

and O, etc., X is a member of the class consisting of hydrogen, halogen,and the methyl radical, and m is 0 or l, and the methyl group in formulaIV can be present in place of any one hydrogen of themono-hydrogen-substituted carbons.

The polyamine can be expressed by the formula hexylene, etc.), thedivalent radical of diethylenc oxide of the formula CH CH OCH -CH etc.);arylene (cg, m-phenylene, p-phenylene, p,p'- hiphcnylenc,dichlorophcnylcnc, hiphcnylene methy lenc of the formula biphenyleneoxide, biphenylene sulfone, biphenylene sulfide, keto biphenylene of theformula etc.), etc. Obviously, the arylene radicals may be attached tonitrogen through the ortho, meta or para positions.

Typical examples of the bisimides which can be employed with thepolyamine compound of formula V are, for instance,N,N-ethylene-bis-maleimide, N,N-mphenylene-bis-maleimide,N,N'-p-phenylene-bismaleimide, N,N'-hexamethylenerbis-maleimide, N,N'-

p,p'-diphenyldimethylsilyl-bis-maleimide, N,N'-p,p'-diphenylmethane-bis-maleimide, N,N diphenylether-bis-maleimide, N,N

diphenylthioether-bis-maleimide, N,N'-diphenylsulfone-bis-maleimide,N,N-dicyclohexyl-methane-bismaleimide, N,N-m-xylylene-bis-maleimide,N,N'-p,p'- benzophenone-bis-maleimide,N,N-(3,3'-dichlorop,p'-biphenylene)bis-maleimide, N,N'-p,p' diphenylether-bis-endomethylene-tetrahydrophthalimide,bisendomethylene-tetrahydrophthalimide, N,N'-p,p-diphenylmethane-bis-tetrahydrophthalimide, etc. Halogenated derivativesof such bisimides where halogen is on the anhydride portion of the imideand on an aryl nucleus can also be employed without departing from thescope of the invention, e.g., N,N'-('3,3'-dichloro-4,4'-biphenyloxy)-bis-maleimide, N,N-(3,3-dibromo-4,4-diphenylmethane)-bis-dichloromaleimide, N,N'-4,4'-diphenylmethane-bis-hexachloroendomethylenetetrahydrophthalimide, etc.

Among the specific polyamines which are useful in connection with thepresent invention, alone or in admixture, are those listed below:

P-xylylene diamine bis(4-amino-cyclohexyl)methane hexamethylene diamineheptamethylene diamine octamethylene diamine nonamethylene diaminedecamethylene diamine ll-methyl-heptamethylene diamine4,4-dimethylheptamethylene diamine 2,l l-diamino-dodecane l,2-bis-(3-amino-propoxy)ethane 2,2-dimethyl propylene diamine3-methoxy-hexamethylene diamine 2,S-dimethylhexarttethylene diamine2,5-dimethylheptamethylene diamine S-methylnonamethylene diamine1,4-diamino-cyclo-hexane l',l Z-diamino-octadecane 2,5-diamino-l,3,4-oxadiazole 2 2)a 2)z 2)a 2 HZN(CH2)3S(CHZ)3NHZ 2 2):i :i)( 2):| 2mctaphenylcnc diamine para-phenylenc diamine 4,4'-diamino-diphenylpropane 4,4-diamino-diphenyl methane benzidine 4,4'-diamino-diphenylsulfide 4,4'-diamino-diphenyl sulfone 3,3'-diamino-diphenyl sulfone4,4'-diamino-diphenyl ether 2,6-diaminopyridinebis(4-amino-phenyl)diethyl silane bis(4-amino-phenyl)diphenyl silanebis(4-amino-phenyl)phosphine oxide 4,4'-diaminobenzophenonebis(4-amino-phenyl)-N-methylamine bis(4-aminobutyl)tetramethyldisiloxanel,5-diaminonaphthalene 3,3-dimethyl-4,4'-diamino-biphenyl 3,3-dimethoxybenzidine 2,4-bis(beta-amino-t-butyl)toluene toluene diaminebis(para-beta-amino-t-butyl-phenyl)etherpara-bis(2-methyl-4-amino-pentyl)benzene para-bis(1,l-dimethyl-5-amino-pentyl)benzene m-xylylene diamine polymethylenepolyaniline of formula NH: NHz

where n is from about 0.1 to 10 and preferably about 0.3.

Useful as the heating element proper of the present invention are any ofthe usual materials used for embedding or impregnating electricalresistive purposes. Among such materials are the various electricalresistance heating wires, carbon particles, carbon impregnated cloth,conductive glass, conductively coated material, and the like, furtherexamples of which will occur to those skilled in the art.

Useful as the laminate structure material are any of various sheet orfabric or mat materials, preferably fabric such as those of asbestos,high-temperatureresistant polyamide or other fibers, glass andcombinations of such materials which can withstand the temperaturesinvolved.

In preparing the present heating unit, the desired number of plies oflaminate material are laid up, the layers being interleaved as desiredwith the heating element proper, whether of wire or other nature. Thelaidup structure is then impregnated with the resin described herein andwrapped or fitted around the structure to be heated to conform closelyto the surface thereof. Alternatively, the laminae can be impregnatedbefore being laid up or interleaved with the heating element. In somecases the most desirable and convenient form may be that of a sheet, inother cases that of a tape, especially where rather irregular or roundedor shouldered surfaces are to be covered. Combinations of tape andsheet, of course, may be used and where one is mentioned, the other isincluded. The impregnated laminate with heating element in place issimply wound as desired about the object such as a reaction vessel to beheated, the heating element being connected to a source of electricpower to cure the resin resistively and provide a permanently durablevessel and heating unit combination. The resin can also be entirely orpartly cured by externally applying heat in any usual manner. I

The following example illustrates the practice of the present invention,it being realized that it is not to be taken as limiting in any way.

Example A resin prepolymer or partially polymerized resin was preparedby placing in a vessel equipped with stirrer, reflux condenser and undernitrogen atmosphere ingredients in the proportion of 164 g of Z-methoxyethyl acetate which was heated to gentle reflux, there was then added29.7 g (0.15 mole) of methylene dianiline followed by 134.3 g (0.37mole) of the bismaleimide of methylene dianiline, the reactiontemperature being maintained at gentle reflux for about 4% hours. Theresultant material was used to impregnate strips of glass cloth laid upin two layers and having therebetween a heating element consisting ofnichrome wire. The flexible laminate so prepared was wrapped about aglass structure and electric current passed through the heating elementwire to provide a temperature of 350F which was maintained for 1 hour.In this particular instance, the part was post-cured in a 250C aircirculating oven for about 17 hours although the electrical resistanceheating is used as well for this post-curing step. After post'curing theheating unit was tightly adhered to the glass base and presented acontinuous, void-free, hard, wear-resistant exterior surface which actedas an efficient source of heat for the unit when connected to anelectrical source.

There are provided by this invention efficient heating units forstructures to be heated which are readily applied in conformablefashion.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, a structure to be heated and an electric heating unitconformably wrapped on said structure for heating thereof, said heatingunit comprising a laminate having embedded therein electric resistiveheating means, said laminate being impregnated with ahigh-temperature-resistant resinous reaction product of unsaturatedbisimide of formula I and polyamine of formula II, curable through saidheating means.

